Write a YAML value (lossless)

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already indicate mutating and idempotent. Description adds valuable context: lossless rewriting, atomicity, and preservation of comments/blanks. No contradiction with annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, front-loaded with core behavior. Every sentence adds unique information: purpose/feature, usage guidance, error behavior. No fluff.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a mutation tool with no output schema, description covers essential aspects: input parameters, behavior (atomic, lossless), error handling. Sufficient for correct agent invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, but description adds examples and constraints for the 'value' parameter (YAML fragment, parse requirement), enhancing understanding beyond schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb ('Set'), resource ('YAML value at a dotted/indexed path'), and key behavior ('lossless', 'atomic'). It clearly distinguishes from sibling 'noyalib_get' by focusing on writing vs reading.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly says when to use ('Renovate-style version bumps and config patches') and recommends reading first with 'noyalib_get'. Also explains behavior on parse error, leaving document unchanged.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.